Why an MHS team?

Gaining insight into the magnetic fields and plasma in solar active regions is very important for studying various solar activities. So far the main approach to obtaining the three-dimensional (3D) magnetic field structure of active regions is to extrapolate the magnetic field from magnetograms measured in the photosphere. A basic assumption in the past was to completely neglect all plasma effects and to perform the so-called force-free field (FFF) extrapolations. A couple of methods (e.g PFSS, linear FFF, nonlinear FFF) are available. Among these methods, till now, the NLFFF performed the best when compared with observations. While the force-free assumption is well justified in the solar corona, it is not the case in the photosphere and chromosphere. New approaches that take into account plasma forces (e.g., plasma pressure and gravity) developed rapidly in the last decade, for example magnetohydrostatic (MHS) extrapolations. It was found that the MHS extrapolation when applied to simple test cases performs better than the NLFFF extrapolation in terms of the accuracy of the reconstructed magnetic field. To calculate the plasma forces correctly, the MHS extrapolation requires a very high-resolution magnetogram (<100 km) which could not be obtained regularly in the past. However, such regular measurements of the magnetic field are possible with the advent of the Daniel K. Inouye Solar Telescope (DKIST). Moreover, the Solar Orbiter (SolO) provides an additional view angle which helps to constrain the magnetic field modelling. We, therefore, gathered an international team to focus on the improvement of the MHS modelling with unprecedented observations. We plan to have two 5-day meetings. The first meeting is expected at the end of 2022 at ISSI-BJ while the second meeting will be held at ISSI a year after the first meeting. Our team will improve the already available magnetic field models which help the solar community to better understand activities in the solar atmosphere.